A display device having a plurality of pixels formed over a substrate has been known. As a typical example of such a display device, a liquid crystal display device, an EL display device, and the like are represented.
An EL display device is a display device having pixels each including a light-emitting element with a structure in which a material exhibiting an electroluminescence (EL) phenomenon is sandwiched by a pair of electrodes. A light-emitting element using an organic compound as a material is called an organic light-emitting element, an organic EL element, or an organic electroluminescent element. A display device having a plurality of such organic light-emitting elements is called an organic EL display device.
An organic EL display device has a plurality of organic light-emitting elements (hereinafter, referred to as light-emitting elements) formed over a substrate, and the light-emitting elements are each controlled by a switching element such as a transistor to display an image. As a substrate, a glass substrate, a metal substrate, a ceramic substrate, or the like can be used, and the use of a flexible substrate such as a substrate including a resin allows the fabrication of a flexible organic EL display device (e.g., US patent application publication No. 2011/0134018).